An acceleration detecting device has been widely used for an existing impact detecting device. For example, the following Patent Document 1 discloses an acceleration detecting device including a bimorph-type acceleration detecting element using piezoelectric ceramics. FIG. 8 is an exploded perspective view illustrating the acceleration detecting device of this type. In FIG. 8, a bimorph-type acceleration detecting element 102 has a strip-like shape. In an acceleration detecting device 101, holding members 103 and 104 are bonded to a pair of opposing side surfaces of the acceleration detecting element 102. That is to say, the pair of holding members 103 and 104 having grooves 13a and 14a opening to the side surfaces of the acceleration detecting element 102 hold the acceleration detecting element 102 therebetween. The thickness of the acceleration detecting element 102 is set to be equal to the thicknesses of the pair of holding members 103 and 104. Accordingly, the acceleration detecting element and the pair of holding members configure a plate-like structure. Further, packaging substrates 105 and 106 are laminated on the upper surface and the lower surface of the above-mentioned plate-like structure in order to seal the acceleration detecting element 102. A recess portion 106a is formed on the inner surface of the packaging substrate 106. It should be noted that a recess portion is also formed on the inner surface of the packaging substrate 105. The recess portion 106a is provided to form a space for not inhibiting vibration of the acceleration detecting element 102.
Patent Document 1: Japanese Unexamined Patent Application Publication No. 9-26433
In the existing acceleration detecting device as disclosed in Patent Document 1, the recess portions are required to be formed on the upper and lower packaging substrates 105 and 106. This makes it difficult to make the thicknesses of the packaging substrates 105 and 106 smaller. Accordingly, there is difficulty in reducing the height of the acceleration detecting device 101. In addition, a process of forming the recess portions is required to be executed, resulting in a problem that the cost is increased.